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Abstract:

Systems and methods are provided for transmitting information between an
intended source and a receiver to minimize co-channel interference from
at least one interfering source. Pilot subcarriers and data subcarriers
may be broadcast from an intended source arid at least one interfering
source. The pilot subcarriers may be shared across base stations or
distributed among base stations in frequency, in time, or both. In
addition, the frequency reuse factor of the pilot subcarriers may be
different than the frequency reuse factor of the data subcarriers. A
receiver receives a composite signal that corresponds with an intended
signal from an intended source and an interfering signal from at least
one interfering source. The portion of the received signal that
corresponds to the intended signal may be recovered by the receiver based
on the broadcast of the pilot subcarriers.

Claims:

1. A method of transmitting information between a first device and a
second device to minimize co-channel interference from at least one
interfering device, the method comprising:broadcasting a plurality of
pilot subcarriers and a plurality of data subcarriers from the first
device and the at least one interfering device, wherein the frequency
reuse of the data subcarriers and the frequency reuse of the pilot
subcarriers are different;receiving a composite signal at the second
device, wherein a portion of the signal corresponds to a first signal
associated with the first device and an interfering signal associated
with the at least one interfering device; andrecovering the portion of
the composite signal that corresponds to the first signal based on the
plurality of pilot subcarriers.

2. The method of claim 1, wherein the frequency reuse of the data
subcarriers is 1/P and the frequency reuse of the pilot subcarriers is
1/P*Q, wherein P and Q are integers greater than 1 and the quantity 1/P
is greater than the quantity 1/P*Q.

3. The method of claim 1, wherein broadcasting the plurality of pilot
subcarriers comprises broadcasting a first pilot subcarrier at a first
frequency band and broadcasting other pilot subcarriers and data
subcarriers at different frequency bands.

4. The method of claim 3, wherein the spectrum of frequency used to
broadcast the plurality of pilot subcarriers is continuous.

5. The method of claim 3, wherein the first frequency band changes after a
period of time.

6. The method of claim 1, wherein broadcasting the plurality of pilot
subcarriers comprises broadcasting a first pilot subcarrier at a first
period of time and broadcasting other pilot subcarriers and data
subcarriers at different periods of time.

7. The method of claim 6, wherein the first period of time changes after a
period of time.

8. The method of claim 1, wherein the plurality of pilot subcarriers
comprises a plurality of orthogonal sequences.

9. The method of claim 8, wherein the plurality of orthogonal sequences
corresponds to the columns of one of a Fourier matrix or a Hadamard
matrix of size N by N, where N is the total number of sources consisting
of the group of the first device and the at least one interfering device.

10. The method of claim 8, wherein broadcasting the plurality of pilot
subcarriers comprises each of the first device and at least one
interfering device broadcasting a pilot subcarrier on at least one
overlapping frequency band.

11. The method of claim 10, wherein broadcasting the plurality of pilot
subcarriers further comprises each of the first device and at least one
interfering device broadcasting a pilot subcarrier on a number of
overlapping frequency bands equal to the total number of sources
consisting of the group of the first device and at least one interfering
device.

12. The method of claim 10, wherein the number of overlapping frequency
bands changes after a period of time.

13. The method of claim 1, wherein each of the plurality of pilot
subcarriers comprises a pseudonoise code sequence.

14. The method of claim 8, wherein each symbol of each of the plurality of
pilot subcarriers is multiplied by a pseudonoise code sequence of a
length equal to the total number of sources consisting of the first
device and at least one interfering device.

15. The method of claim 1, further comprising estimating intended channel
information associated with the first device.

16. A system for transmitting information between a plurality of sources
and a second device to minimize co-channel interference from the
plurality of sources, the system comprising:a first device and at least
one interfering device configured to broadcast a plurality of pilot
subcarriers and a plurality of data subcarriers from the first device and
the at least one interfering device, wherein the frequency reuse of the
data subcarriers and the frequency reuse of the pilot subcarriers are
different; anda second device configured to:receive a composite signal,
wherein a portion of the signal corresponds to a first signal associated
with the first device and an interfering signal associated with the at
least one interfering device; andrecover the portion of the received
signal that corresponds to the first signal based on the plurality of
pilot subcarriers.

17. The system of claim 16, wherein the frequency reuse of the data
subcarriers is 1/P and the frequency reuse of the pilot subcarriers is
1/P*Q, wherein P and Q are integers greater than 1 and the quantity 1/P
is greater than the quantity 1/P*Q.

18. The system of claim 16, wherein the first device and at least one
interfering device are further configured to broadcast a first pilot
subcarrier at a first frequency band and broadcasting other pilot
subcarriers and data subcarriers at different frequency bands.

19. The system of claim 18, wherein the spectrum of frequency used to
broadcast the plurality of pilot subcarriers is continuous.

20. The system of claim 18, wherein the first frequency band changes after
a period of time.

21. The system of claim 16, wherein the first device and at least one
interfering device are further configured to broadcast a first pilot
subcarrier at a first period of time and other pilot subcarriers and data
subcarriers at different periods of time.

22. The system of claim 21, wherein the first period of time changes after
a period of time.

23. The system of claim 16, wherein the plurality of pilot subcarriers
comprises a plurality of orthogonal sequences.

24. The system of claim 23, wherein the plurality of orthogonal sequences
corresponds to the columns of one of a Fourier matrix and a Hadamard
matrix of size N by N, where N is the total number of sources consisting
of the group of the first device and at least one interfering device.

25. The system of claim 23, wherein each of the first device and at least
one interfering device is further configured to broadcast a pilot
subcarrier on a least one overlapping frequency band.

26. The system of claim 25, wherein each of the first device and at least
one interfering device is further configured to broadcast a pilot
subcarrier on a number of overlapping frequency bands equal to the total
number of sources consisting of the group of the first device and at
least one interfering device.

27. The method of claim 25, wherein the number of overlapping frequency
bands changes after a fixed period of time.

28. The system of claim 16, wherein each of the plurality of pilot
subcarriers comprises a pseudonoise code sequence.

29. The system of claim 23, wherein each symbol of each of the plurality
of pilot subcarriers is multiplied by a pseudonoise code sequence of a
length equal to the total number of sources consisting of the first
device and at least one interfering device.

30. The system of claim 15, wherein the second device is further
configured to estimate intended channel information associated with the
first device.

31. A mobile device that minimizes the effect of co-channel interference
on a received composite signal, wherein at least a portion of the signal
corresponds to a first signal associated with a first device and an
interfering signal associated with at least one interfering device, the
mobile device comprising signal processing circuitry configured to:detect
a plurality of pilot subcarriers and a plurality of data subcarriers in
the received signal;analyze the pilot sequence of at least one of the
plurality of pilot subcarriers to determine an interference channel gain
between the mobile device and at least one of the interfering devices
that broadcast the at least one pilot subcarrier; andrecover the portion
of the received signal that corresponds to the first signal based on the
interference channel gain and the plurality of pilot subcarriers, wherein
the frequency reuse of the data subcarriers and the frequency reuse of
the pilot subcarriers are different.

32. The mobile device of claim 31, wherein the frequency reuse of the data
subcarriers is 1/P and the frequency reuse of the pilot subcarriers is
1/P*Q, wherein P and Q are integers greater than 1 and 1/P is greater
than 1/P*Q.

33. The mobile device of claim 31, wherein the plurality of pilot
subcarriers comprises a plurality of orthogonal sequences.

34. The mobile device of claim 33, wherein the signal processing circuitry
is further configured to demodulate the composite signal using a Fast
Fourier Transform.

35. The mobile device of claim 31, wherein each of the plurality of pilot
subcarriers comprises a pseudonoise code sequence.

36. The mobile device of claim 31, wherein the signal processing circuitry
is further configured to detect whether the plurality of pilot
subcarriers were distributed in at least one of frequency, time, or both.

37. The mobile device of claim 31, wherein the signal processing circuitry
is further configured to detect whether the whether the plurality of
pilot subcarriers were shared across at least one first device and
interfering device.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This claims the benefit under 35 U.S.C. §119(e) of U.S.
Provisional Application No. 60/955,948 filed Aug. 15, 2007, which is
hereby incorporated herein by reference in its entirety.

BACKGROUND

[0002]The following relates generally to transmitting information between
an intended source and a receiver in a communication system, and more
particularly to designs for frequency reuse and pilot subcarriers to
minimize co-channel interference during transmission from other sources
that cause interference.

[0003]There are several conventional techniques to increase the throughput
of a wireless network. These techniques aim to expand the amount of
information that can be transmitted over the network while minimizing the
probability that errors will occur during transmission. One of these
techniques is frequency reuse, which entails using the same frequency on
a network for multiple simultaneous transmissions. Most wireless
communication systems are designed to achieve a frequency reuse of one,
which is often referred to as the "universal" frequency reuse factor. A
frequency reuse of one means that the source, or base station, for each
cell in the network uses the same set of frequencies simultaneously for
the transmission of information. However, in wireless systems it is
challenging to achieve a frequency reuse of one because of the co-channel
interference presented by the sources of adjacent cells. Thus, separate
communication techniques may be used in the transmission of information
in order to differentiate the information transmitted by the source in
each cell.

[0004]One of the techniques used to reduce co-channel interference is
orthogonal frequency-division multiplexing (OFDM). OFDM is a digital
multi-carrier modulation scheme which uses a large number of
closely-spaced subcarriers comprised of an orthogonal set of data symbols
to transmit information. These subcarriers typically overlap in
frequency, but are separated using algorithms such as a Fast Fourier
Transform. Each subcarrier is typically modulated with a conventional
modulation scheme, such as quadrature amplitude modulation or amplitude
and phase-shift keying, in order to maintain a data rate similar to a
single-carrier modulation scheme.

[0005]Traditional OFDM requires estimating the channel to determine
co-channel interference between sources. However, in order to determine
the interference between sources, one must know the parameters of the
channel used for transmission. This requisite knowledge presents a
problem for cellular communication systems achieving a frequency reuse of
one results in co-channel interference that makes it harder to estimate
the parameters of the channel, while using a multi-carrier modulation
scheme such as OFDM to eliminate the co-channel interference requires
knowing the parameters of the channel.

SUMMARY OF THE DISCLOSURE

[0006]Accordingly, systems and methods are disclosed for transmitting
information between sources and receivers to maximize throughput while
minimizing co-channel interference. These systems and methods enable
wireless communication to occur more reliably without having to waste the
precious resource of throughput in a network.

[0007]The disclosed embodiments can be employed in any suitable wireless
communications system, such as a cellular system, (e.g., a mobile
network) or a wireless Internet system (e.g., a WiMAX network) that
include a plurality of devices or systems. Using a cellular system as an
example, the cellular system may include a plurality of sources, or base
stations, that can each communicate with receivers, or mobile stations
(e.g., cellular telephones), that are within an area assigned to that
base station. When a mobile station is connected to the cellular network,
however, the mobile station may receive radio signals from not only an
intended source (e.g., the base station assigned to cover the area that
the mobile station is located in), but from one or more interfering
sources (e.g., adjacent or neighboring base stations transmitting data to
other mobile stations). Thus, the mobile, station may be configured to
decode a received signal in a manner that takes into account not only
characteristics of the intended source, but also any interfering sources.

[0008]The intended source and interfering sources may broadcast separate
signals for both data and pilot sequences known as "data subcarriers" and
"pilot subcarriers", respectively. A particular base station might not
use one or more of the subcarrier frequencies available to transmit pilot
patterns or data. These frequency bands may be referred to as "unused
subcarriers". The data sequences may include information transmitted
through the network, while the pilot sequences may include channel
information, for a particular area of transmission. The pilot and data
subcarriers may be broadcast over distinct bands of frequency. In order
to maintain a frequency reuse of one for the data subcarriers while
avoiding co-channel interference, the pilot subcarriers and the data
subcarriers may be broadcast with different factors of frequency reuse.
For example, the frequency reuse of the data subcarriers may be one while
the frequency reuse of the pilot subcarriers may be a fractional number.
This transmission scheme compromises true universal frequency reuse, but
allows for the design of the pilot subcarriers to allow for better
estimation of the channel.

[0009]The intended source and interfering sources may broadcast the pilot
subcarriers with a particular design to minimize the effects of
co-channel interference. This design may include distributing pilot
subcarriers among multiple base stations. The pilot subcarriers may be
distributed in frequency, in time, or both. This design may also include
sharing pilot subcarriers across multiple base stations. The pilot
subcarriers may include orthogonal sequences. In addition, the pilot
subcarriers may include pseudonoise code sequences. The pseudonoise code
sequences may be used as the symbols for the pilot subcarriers, or the
pseudonoise code sequences may be applied to each symbol of an existing
pilot sequence.

[0010]A mobile station may receive a signal that corresponds to both an
intended signal associated with the intended source and an interfering
signal associated with interfering sources. The mobile station may detect
the pilot subcarriers and data subcarriers in the received signal, and
estimate channel information associated with the interfering sources. The
channel information may allow the mobile station to determine which
portion of the received signal corresponds to the interfering signal. The
mobile station can make this determination by analyzing a pilot
subcarrier received from an interfering source. From the pilot sequence
of the pilot subcarrier, the mobile station may determine an interference
channel gain (e.g., magnitude and phase of the gain) associated with the
physical space between the mobile station and the interfering source.
Alternatively, the mobile station may compute just magnitude information
for the interference channel gain, such as an average magnitude square or
an instantaneous magnitude square of the interference channel gain.

[0011]The mobile station may use the estimated channel information to
recover the portion of the received signal that corresponds to the
interfering signal. This recovery may be based on the design of the pilot
subcarriers broadcast by the intended source and the at least one
interfering source. The recovery may be based on the fact that the
frequency reuse of the data subcarriers and the frequency reuse of the
pilot subcarriers are different, that the pilot subcarries include
orthogonal sequences, and/or that the pilot subcarriers include
pseudonoise code sequences. For example, the frequency reuse of the data
subcarriers may be 1/P and the frequency reuse of the pilot subcarriers,
may be 1/P*Q, wherein P and Q are integers greater than 1 and 1/P is
greater than 1/P*Q.

[0012]The mobile device, may be able to detect whether the pilot
subcarriers are distributed in at least one of frequency, time, or both.
In addition, the mobile device may be able to detect whether the pilot
subcarriers are shared across devices. Each of these functions may be
performed by appropriate signal processing and/or control circuitry of
the mobile device. If the pilot subcarriers are shared across base
stations and include orthogonal sequences, the receiver may use a forward
Fast Fourier Transform to demodulate the signal and recover the
originally transmitted information.

BRIEF DESCRIPTION OF THE FIGURES

[0013]The above and other aspects and advantages of the invention will be
apparent upon consideration of the following detailed description, taken
in conjunction with the accompanying drawings, in which like reference
characters refer to like parts throughout, and in which:

[0014]FIG. 1 is a diagram of three radio cells of an illustrative cellular
system;

[0015]FIG. 2 is a block diagram of an illustrative base station
transmitter;

[0016]FIG. 3 is a block diagram of an illustrative mobile station
receiver;

[0017]FIG. 4 is a diagram of an illustrative scheme for distributing pilot
subcarriers over frequency;

[0018]FIG. 5 is a diagram of an illustrative scheme for distributing pilot
subcarriers over frequency and shifting the distribution over time;

[0019]FIG. 6 is a diagram of an illustrative scheme for distributing pilot
subcarriers over time;

[0020]FIG. 7 is a diagram of an illustrative scheme for sharing pilot
subcarriers across multiple base stations;

[0021]FIG. 8 shows a flow diagram of an illustrative process for
transmitting information between an intended source and a receiver to
minimize co-channel interference from interfering sources;

[0022]FIG. 9 is a block diagram of an exemplary hard disk drive that can
employ the disclosed technology;

[0023]FIG. 10 is a block diagram of an exemplary digital versatile disc
that can employ the disclosed technology;

[0024]FIG. 11 is a block diagram of an exemplary cell phone that can
employ the disclosed technology;

[0025]FIG. 12 is a block diagram of an exemplary set top box that can
employ the disclosed technology; and

[0026]FIG. 13 is a block diagram of an exemplary media player that can
employ the disclosed technology.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0027]FIG. 1 shows a simplified diagram of illustrative cellular system
100. Cellular system 100 can include a plurality of base stations that
are interconnected to form a mobile or cellular network. These base
stations can include base stations 122, 142, and 162. Each of these base
stations can be configured to communicate with mobile stations located
within a particular physical area within that base station's radio
communications range. The physical area may be referred to as a radio
cell. In particular, base station 122 may communicate with mobile
stations within radio cell 120, base station 142 may communicate with
mobile stations within radio cell 140 (e.g., mobile stations 144 and
146), and base station 162 may communicate with mobile stations within
radio cell 160 (e.g., mobile station 164). In FIG. 1, radio cells 120,
140, and 160 are represented by hexagonal regions, although this shape is
merely illustrative.

[0028]Mobile stations 144, 146, and 164 may be any suitable type of
cellular telephone compatible with the base stations of the mobile
network. For example, mobile stations 144, 146, and 164 can operate based
on a protocol or communications standard compatible with base stations
122, 142, and 162. The base stations and mobile stations, of cellular
system 100 can operate using any suitable conventional cellular protocol,
such as the Global Systems for Mobile communications ("GSM") standard a
code division multiple access ("CDMA") based standard, an orthogonal
frequency-division multiple access ("OFDMA") based standard (such as
WiMAX), or using a non-conventional protocol.

[0029]The base stations and mobile stations in cellular system 100 may use
any of a variety of modulation and coding schemes to enable reliable
communication. For example, base stations 122, 142, and 162 may operate
with a modulation scheme based on orthogonal frequency division
multiplexing ("OFDM"). Further examples of suitable modulation and coding
schemes will be discussed in detail below in connection with FIGS. 2 and
3. To notify the mobile stations of the modulation and coding used by a
base station, base stations 122, 142, and 162 may broadcast a control
sequence to at least the mobile stations within their respective radio
cells. This control sequence may be in the form of a pilot sequence, or
pilot pattern. In addition to coding and modulation information, the
control sequence may also include any other suitable control information
that the mobile stations may use to interpret the data sent by a base
station. For example, the control sequence may include information on how
the data frames are structured, how many symbols are included in each
frame, and the intended recipient (e.g., mobile station) of the next data
block.

[0030]Base stations 122, 142, and 162 may transmit a pilot pattern or
sequence to each mobile station within its radio cell to provide each
mobile station with, among other things, phase alignment information. The
pilot pattern may be based on a particular pseudo-noise ("PN") sequence,
and each base station may utilize a different PN sequence. The different
PN sequences may allow the mobile stations (e.g., mobile station, 144) to
identify the base station associated with a received pilot pattern.

[0031]Base stations 122, 142, and 162 may broadcast the pilot pattern or
sequence and network data to all mobile stations that are within radio
communication range. This allows each base station to not only transmit
information to any mobile station within that base station's radio cell,
but also to mobile stations in neighboring radio cells that are
sufficiently close to the base station. For example, due to the proximity
of mobile station 144 to base station 142 in radio cell 140, mobile
station 144 may predominantly receive information from base station 142.
Mobile station 146, on the other hand, may be able to receive information
not only from base station 142 in radio cell 140, but may also receive
interfering information from base station 162 in neighboring radio cell
160. The pilot pattern of sequence and the network data may be
transmitted on a separate signal carried on the main transmission of base
stations 122, 142, and 162. These separate transmissions may be referred
to as subcarriers. Each subcarrier may be transmitted, on a distinct
frequency band, or they may be transmitted on overlapping frequency
bands. If base stations 142 and 162 operate using subcarrier frequencies
such that signals received from these two sources are not easily
distinguishable, mobile station 146 may suffer from an effect referred to
sometimes as "inter-cell co-channel interference" (or simply "co-channel
interference" or "interference").

[0032]For simplicity, the radio signal expected by mobile station 146
(e.g., from base station 142, or the "intended source") may sometimes be
referred to as the "intended signal," and the channel, gain of the
corresponding channel (e.g., the "intended channel") may sometimes be
referred by the symbol, hk. The radio signal from a neighboring
mobile station (e.g., from base station 162, or the "interfering source")
may sometimes be referred to as the "interference signal," and the
channel gain of the corresponding channel (e.g., the "interference
channel") may sometimes be represented by the symbol, gk.

[0033]In many scenarios, the co-channel interference (e.g., the effect of
base station 162 on mobile station 146) may be a stronger than any noise
that may occur during, data transmission from, base station to mobile
station. This may be especially true when a mobile station is near the
boundary of two radio cells. In conventional communications protocols,
co-channel interference is circumvented by having neighboring base
stations broadcast network data using different frequency channels. For
example, if cellular system 100 were to operate using one of these
conventional protocols, the mobile network can assign a first frequency
channel to base station 122 and radio cell 120, a second frequency
channel to base station 142 and radio cell 140, and a third frequency
channel to base station 162 and radio cell 160. By having neighboring
base stations use different frequency channels, a mobile station in a
particular radio cell can suffer from little to no interference from a
base station in a neighboring radio cell. For example, in this scenario,
even though mobile station 146 may be able to receive an interference
signal from neighboring base station 162, mobile station 146 can tune
into only the frequency channel of base station 142 to ensure that radio
signals from base station 162 are substantially excluded.

[0034]In some embodiments, each radio cell of Cellular system 100 may be
further broken up into physical regions referred to sometimes as sectors,
and current protocols can assign each of the sectors a different
frequency channel. Radio cells may be decomposed into any suitable number
of sectors (e.g., 2-10 sectors). For example, radio cell 120 may be
decomposed into three sectors: sector 130, sector 132, and sector 134.
Likewise, radio cell 140 may be decomposed into sector 150, sector 152,
and sector 154 and radio cell 160 may be decomposed into sector 170, 174,
and 176. In current protocols, each of these sectors may be assigned to a
different or the same frequency channel by the mobile network. For
example, the mobile network may assign each of the three sectors in radio
cells 120, 140, and 160 to different frequency channels such that no
neighboring sector uses the same frequency channel. As with the example
above, where each radio cell is assigned to a different frequency, this
scenario also allows the mobile stations to decode received signals
without concern for interference effects.

[0035]The communications technique of assigning neighboring base stations
or sectors different frequency bands may be referred to as frequency
reuse. Cellular system 100 may, as described above, use three different
frequency channels to implement frequency reuse. Such a communications
system may be referred to as having a frequency reuse of 1/3.

[0036]While frequency reuse reduces interference, frequency reuse does not
efficiently utilize the bandwidth made available to cellular systems.
That is, cellular systems are assigned a limited amount of bandwidth.
With each base station using only a fraction of the available bandwidth,
each base station has a spectral efficiency (and therefore a maximum data
rate) that is well below the possible spectral efficiency and data rate
that can be achieved. Accordingly, as described in greater detail below,
embodiments include techniques that enable greater frequency reuse. These
techniques may be used with conventional communication protocols such as
OFDM. Further, techniques are provided that can counter the effects of
inter-cell co-channel interference such that using different frequency
channels in neighboring radio cells or sectors is unnecessary.

[0037]While some embodiments of the present invention are described in
terms of a cellular system, such as cellular system 100, this is merely
illustrative. The techniques, features, and functionalities of the
embodiments may be applied to other suitable communications systems, such
as wifi and wireless Internet systems (e.g., WiMAX systems).

[0038]FIG. 2 shows a simplified block diagram of base station transmitter
200 that can prepare network information 210 for transmission as radio
signal 270. In some embodiments, base station transmitter 200 may be
implemented as the transmitter for one or more of base stations 122, 142,
and 162 of FIG. 1. Base station transmitter 200 can include encoder 220,
interleaver 240, and modulator 260.

[0039]Encoder 220 may encode network information 210 based on a suitable
error correcting code ("ECC"). For example, encoder 220 may operate using
a convolutional code (e.g., a rate-1/2 or rate-2/3 convolutional code) of
memory m. Encoder 220 may therefore convert network information 210,
which may be some form of digital information (e.g., a stream of binary
data), into an encoded stream of binary data. Since encoder 220 may have
a memory of m, each m consecutive bits in the encoded stream created by
encoder 220 depends on the value of the same one bit of network
information 210. In order to remove any negative effects that may result
from this dependency (e.g., the inability to reliably decode when burst
errors are present), the encoded stream may be interleaved by interleaver
240. In particular, interleaver 240 may change the order of the bits in
the encoded stream to ensure that neighboring bits in the interleaved
sequence are effectively independent of each other.

[0040]Modulator 260 of base station transmitter 200 may be configured to
convert the interleaved digital sequence produced by interleaver 240 into
a signal for transmission. Modulator 260 may first group bits of the
interleaved sequence into symbols based on the size of a modulation
scheme, and may then modulate the symbols into a signal having a
particular magnitude and phase specified by the modulation scheme.
Modulator 260 may use any suitable modulation scheme of any of a variety
of sizes. For example, modulator 260 may utilize a quadrature amplitude
modulation ("QAM") scheme (e.g., 4 QAM, 16 QAM, 32 QAM) or a phase shift
keying ("PSK") modulation scheme (e.g., QPSK, 16 PSK, 32 PSK).

[0041]The particular modulation scheme employed by modulator 260 may be
designed to operate effectively with the particular error correcting code
(ECC) employed by encoder 200. This type of communications technique is
commonly referred to as coded modulation. Therefore, as base station
transmitter 200 of FIG. 2 also includes interleaver 240, the overall
communications technique employed by base station transmitter 200 can be
referred to as bit-interleaved coded modulation ("BICM").

[0042]Modulator 260 may produce radio signal 270 for transmission to one
or more mobile stations (e.g., mobile stations 144, 146, or 162). Radio
signal 270 may sometimes be represented by the variable, x. At some time,
k, radio signal 270 may represent a symbol of encoded/interleaved network
information 210, and at some time, k+1, radio signal 270 may represent
the next symbol of encoded/interleaved network information 210. For
simplicity, the variable xk will be used below to represent the
value of radio signal 270 when sampled at a particular time, k. In some
embodiments, k represents another type of dimension of radio signal 270
other than time, such as a spatial dimension or frequency dimension.

[0043]Radio signal 270 may be subject to noise (e.g., random noise or
signal-dependent noise) during data transmission from base station
transmitter 200 to a mobile station. In some scenarios, radio signal 270
may also be subject to co-channel interference, that further distorts
radio signal 270. Thus, even though radio signal 270 is transmitted, the
radio signal actually received by a mobile station receiver may be
considerably different from radio signal 270.

[0044]FIG. 3 shows a simplified block diagram of mobile station receiver
300. In some embodiments, mobile station receiver 300 may be implemented
as part of one or more mobile stations 144, 146, and 164. Mobile station
receiver 300 can be configured to receive and decode a noisy or distorted
version of radio signal 270 (FIG. 2). In particular, mobile station
receiver 300 may receive radio signal 370, which may be radio signal 270
after being affected by random or signal-dependent noise and inter-cell
co-channel interference. Radio signal 370 may sometimes be represented by
the variable, yk for some time, k. Mathematically, radio signal 370
may be given by,

yk=hk-i xk+vk. (EQ. 1)

In EQ. 1, hk is the channel gain that represents the magnitude and
phase effect of the intended channel, and vk may represent both the
noise and interference affecting radio signal 270.

[0045]Since vk in EQ. 1 may be a combination of noise and
interference, EQ. 1 may be re-written as,

yk=hkxk+wk+zk, (EQ. 2)

where zk constitutes the noise component of vk, and wk
constitutes the interference component of vk. Finally, as the
interference signal may be associated with an interference channel gain,
gk (as described above in connection with FIG. 1), EQ. 2 may be
rewritten as,

yk=hkxk+gksk+zk. (EQ. 3)

Here, sk may be a radio signal that represents a symbol that the
interfering base station intends to transmit to a different mobile
station. Note that sk may be associated with a modulation scheme
with a different number of signal constellation points, of differing
magnitudes, and with a different symbol-to-signal point mapping.

[0046]Mobile station receiver 300 can be configured to decode radio signal
370 and obtain an estimate of the originally transmitted information
(e.g., network information 210 of FIG. 2). To decode radio signal 370,
mobile station receiver 300 can include demodulator 360, de-interleaver
340, and decoder 320. Each of these receiver components may correspond to
a transmitter component in base station transmitter 200 and may
effectively undo the operation performed by the corresponding transmitter
component. For example, demodulator 360 may correspond to modulator 260
that can demodulate/de-map radio signal 370 using at least the modulation
scheme and signal constellation set as modulator 260. De-interleaver 340
may correspond to interleaver 240 and may return the order of the
received data into its original order, e.g., the order expected by
decoder 320. Decoder 320 may be a soft-decoder that corresponds to
encoder 220, and may perform decoding based on the same error correcting
code (e.g., convolutional code) as encoder 220. Thus, decoder 320 may
produce estimate 310 of network information (e.g., network information
210). If mobile station 300 successfully interprets radio signal 370,
estimate 310 may be the same digital sequence as network information 210.

[0047]Mobile station receiver 300 of FIG. 3 can compute soft information
for received signal 370 using accurate channel and modulation information
for the interfering source. Using more than just the power of the noise
and interference, demodulator 360 can compute a considerably more
reliable and accurate log-likelihood ratio or other soft metric. To
compute the channel information, estimate, mobile station receiver 300
may, for example, include computational logic (not shown) that is
configured to estimate the interference channel gain. The computational
logic may also be configured to compute the intended channel gain. The
computational logic may compute these channel information estimates by
analyzing the characteristics of pilot patterns received from each
source. This analysis may be based on the particular design of the pilot
patterns broadcast by the base stations. In one example, if each source
broadcasts a pilot pattern based oh an orthogonal sequence, the
computational logic can distinguish between the different pilot patterns.
In another example, if each source broadcasts a pilot pattern based on a
unique PN sequence, the computational logic can distinguish between the
different pilot patterns. From the analysis of various pilot patterns,
the computational logic produces an estimate of the interference and/or
intended channel gain, for example. Mobile station receiver 300 may
compute the channel information estimates at any suitable time during
operation, such as at power-up, when initially connected to a base
station, periodically, whenever the pilot sequence is transmitted, etc.
The improved estimates of the soft information may allow decoder 320 to
produce more accurate estimates of network information 310.

[0048]Referring now to FIGS. 4-7, various illustrative schemes for the
broadcast of pilot subcarriers are shown. As mentioned above with respect
to FIG. 3, a particular design for the pilot subcarriers broadcast by the
base stations, such as the intended source and the interfering sources,
in the cellular communication system can allow the mobile station
receiver to distinguish between the different pilot patterns. This
separation of the pilot patterns at the mobile station receiver allows
for better estimation of the channel, which ultimately leads to a more
accurate recovery of the portion of the received signal that corresponds
to the intended signal. Each of these illustrative schemes shows
broadcast subcarriers for three base stations. However, this number is
merely illustrative, as each of the schemes shown in FIGS. 4-7 may be
employed by any number of base stations, such as 5, 10, 50, 100, 500,
1000, 5000, or more than 5000 base stations. In addition, the number of
subcarriers shown in FIGS. 4-7 is merely illustrative, as there may be
any number of subcarriers broadcast by a base station, such as 5, 10, 50,
100, 500, 1000, 5000, or more than 5000 subcarriers. Further, each of the
subcarriers of a particular base station in FIGS. 4-7 may be aligned in
frequency with the subcarriers of another base station, or may be
overlapping in frequency with the subcarriers of another base station.

[0049]Referring to FIG. 4, a diagram of an illustrative scheme 400 for
distributing pilot subcarriers over frequency is shown. In scheme 400, a
distinct pilot pattern or sequence is broadcast by each base station 410,
420, and 430 in a distinct set of pilot subcarriers 416, 426, and 436.
Further, the pilot subcarriers are broadcast across each of the base
stations 410, 420, and 430 with a frequency reuse factor that is
different than the frequency reuse factor used to broadcast the data
subcarriers 412, 422, and 432. As shown in scheme 400, the frequency
reuse factor of the pilot subcarriers is fractional (in this case 1/3),
while the frequency reuse factor of the data subcarriers is equal to one.
Thus, scheme 400 sacrifices universal frequency reuse to eliminate
potential co-channel interference in the received signal at the receiver.

[0050]Further, in scheme 400 each pilot subcarrier for each base station
is broadcast at a unique range of frequencies. Thus, scheme 400 can
include unused subcarriers 414, 424, and 434, each of which correspond to
a pilot subcarrier of another base station 410, 420, and 430. For
example, base station 430 may not broadcast a data subcarrier or pilot
subcarrier in the frequencies used by pilot subcarrier 416 of base
station 410 and pilot subcarrier 426 of base station 420. Although scheme
400 shows unused subcarriers 414, 424, and 434 as being adjacent in
frequency to pilot subcarriers 416, 426, and 436, unused subcarriers 414,
424, and 434 may be nonadjacent in frequency to pilot subcarriers 416,
426, and 436.

[0051]A mobile station receiver (e.g. mobile station receiver 300 of FIG.
3) can receive a signal with the superimposition of all of the
subcarriers broadcast from base stations 410, 420, and 430. Thus,
assuming that the subcarriers are aligned in frequency between each base
station 410, 420, and 430, distinguishing between the pilot subcarriers
may require no further design considerations in the broadcast of the
pilot subcarriers 416, 426, and 436. However, if the subcarriers are not
aligned in frequency, further design considerations may be needed in the
broadcast of the pilot subcarriers. These design considerations will be
discussed with respect to FIG. 7 below.

[0052]The pattern of unused subcarriers and pilot subcarriers may repeat
at a particular band of frequencies among the subcarriers broadcast in
each base station 410, 420, and 430. These repetitions of the pattern of
unused subcarriers and pilot subcarriers may allow for greater redundancy
of information about the pilot pattern or sequence at the mobile station
receivers, and thus provide for fewer errors in the estimate of the
network information provided by analysis of data subcarriers 412, 422,
and 432.

[0053]Referring now to FIG. 5, a diagram of an illustrative scheme 500 for
distributing pilot subcarriers over frequency and shifting the
distribution over time is shown. In scheme 500, the pattern of data
subcarriers, pilot subcarriers, and unused subcarriers 512, 522, and 532
may shift in frequency in each base station 510, 520, and 530 after a
particular period of time, forming a new pattern of subcarriers 514, 524,
and 534. The period of time could be any time period, such as one
nanosecond, one microsecond, one millisecond, or greater than one
millisecond. These shifts may be regular, meaning that they occur every
time period, or they may occur according to any particular pattern in
time. For example, a particular pattern of data subcarriers, pilot
subcarriers, and unused subcarriers 512, 522, or 532 may shift in
frequency every two time periods, followed by another shift in frequency
after one time period. In addition, the shift in frequency may be the
same during every shift, or may vary according to any particular pattern.
Such a pattern in shifting can allow a mobile station receiver (e.g.
mobile station receiver 300 in FIG. 3) to distinguish between pilot
subcarriers more quickly and efficiently if certain frequencies are
inundated with interference or are unusable for transmission due to
environmental or network conditions.

[0054]In certain embodiments, the shifts in frequency will be coordinated
between base stations 510, 520 and 530. That is, the shifts in frequency
will occur such that the location of the pilot subcarrier in frequency
will always be aligned in frequency with unused subcarriers across all
base stations 510, 520, and 530. This coordination ensures that a mobile
station receiver (e.g. mobile station receiver 300 in FIG. 3) will be
able to distinguish between pilot subcarriers, barring any misalignment
of the subcarriers in frequency.

[0055]Referring now to FIG. 6, a diagram of an illustrative scheme 600 for
distributing pilot subcarriers over time is shown. In scheme 600, the
pilot patterns broadcast by base stations 610, 620, and 630 are staggered
in time by a particular time period as shown by patterns 612, 622, and
632. For example, base station 610 broadcasts pilot subcarrier P1 at time
t0, again at time t3, and then every two time periods thereafter; base
station 620 broadcasts pilot subcarrier P2 at time t1, again at time t4,
and every two time periods thereafter; and base station 630 broadcasts
pilot subcarrier P3 at time t2, again at time t5, and every two time
periods thereafter. In addition, each base station 610, 620, and 630
broadcasts their pilot subcarriers at the same set of frequencies. In
this fashion, the broadcast of the pilot subcarriers takes up a minimal
amount of bandwidth while allowing a mobile station receiver (e.g. mobile
station receiver 300 in FIG. 3) to distinguish between received pilot
subcarriers.

[0056]In certain embodiments, patterns 612, 622, and 632 may repeat at a
particular band of frequencies among the subcarriers broadcast in each
base station 610, 620, and 630. In addition, patterns 612, 622, and 632
may shift frequency simultaneously after a particular period of time
similar to scheme 500 discussed with respect to FIG. 5.

[0057]By transmitting a particular pilot subcarrier sparsely in time,
scheme 600 may only toe useful in certain systems where a copy of the
pilot pattern is not constantly needed for channel detection. However,
scheme 600 has the advantage of providing the base stations with extra
subcarriers for broadcasting data subcarriers, thus increasing the
overall throughput of the system.

[0058]Referring now to FIG. 7, a diagram of an illustrative scheme 700 for
sharing pilot subcarriers across multiple base stations is shown. In
scheme 700, base stations 710, 720, and 730 broadcast pilot subcarriers
712, 722, and 732 at the same of overlapping set of frequencies. The
individual pilot subcarriers P1, P2, and P3 may be broadcast any number
of times depending on the desired redundancy for the data broadcast on
the channel. For example, as shown in scheme 700 the pilot subcarriers
P1, P2, and P3 are each broadcast three times. In addition, in scheme 700
it is preferable that pilot subcarriers 712, 722, and 732 are adjacent in
frequency.

[0059]The design choice of sharing pilot subcarriers may be combined with
any of the designs previously discussed--for example, schemes 500 and
600. For example, the pilot subcarriers 712, 722, and 732 may shift
frequencies simultaneously after a particular period of time similar to
scheme 500 discussed with respect to FIG. 5. In another example, pilot
subcarriers 712, 722, and 732 may be staggered in time similar to scheme
600 discussed with respect to FIG. 6. In addition, pilot subcarriers 712,
722, and 732 may repeat at a particular band of frequencies among the
subcarriers in each base station 710, 720, and 730.

[0060]A mobile station receiver (e.g. mobile station receiver 300 of FIG.
3) can receive a signal with the superimposition of all of the
subcarriers broadcast from base stations 710, 720, and 730. Because the
pilot subcarriers 712, 722, and 732 broadcast by base stations 710, 720,
and 730 may overlap at least partially in frequency, the mobile station
receiver may not be able to distinguish between the shared pilot
subcarriers P1, P2, and P3 without using further techniques to design the
shared pilot subcarriers.

[0061]In order for a mobile station receiver to distinguish between the
shared pilot subcarriers, they can be designed to include orthogonal
sequences. For example, in scheme 700 where there are three transmitting
base stations in the network and assuming that the symbols are binary
numbers, P1 could be the sequence [1 1 1], P2 could be the sequence [1 1
0]. and P3 could be the sequence [0 0 1]. In another example, where there
are three base stations in the network and assuming that the symbols are
complex numbers, P1 could be the sequence [1 1 1], P2 could be the
sequence [1 e.sup.j2π/3 e.sup.j4π/3], and P3 could be the sequence
[1 e.sup.j4π/3 e.sup.j2π/3]. Further, orthogonal sequences for a
network with N base stations, where N is any number, may be the columns
of the Fourier matrix of size N by N. In addition, orthogonal sequences
for a network with N base stations, where N is an even number, may be the
columns of the Hadamard matrix of size N by N.

[0062]In order for channel estimation to be successful using shared pilot
subcarriers designed to include orthogonal sequences, it is important
that the characteristics of the channel remain constant over a period of
time corresponding to the length of the orthogonal sequence. If the
characteristics of the channel change over this period of time, it will
be difficult for the mobile receiver to distinguish between the
orthogonal sequences in the received pilot subcarriers.

[0063]Further, in order for a mobile station receiver to distinguish
between shared pilot subcarriers, they can be designed to include a
sequence of data symbols generated from a pseudonoise (PN) code. This
design may be particularly useful to distinguish between broadcast pilot
subcarriers when the number of base stations in the network is on the
order of hundreds or thousands, or where there are large differences in
the power of the transmission from the intended source as compared to the
interfering sources. A PN code has a range of values similar to those of
a random sequence of symbols, but the symbols are deterministically
generated. Examples of PN codes may include maximal length sequences,
Gold codes, Kasami codes, and Barker codes. A pseudonoise code may be
applied to each symbol in the pilot subcarrier. For example, suppose that
there are N base stations in the network, each of which broadcast a pilot
sequence that is N symbols in length. Assuming the pilot sequence is
binary, each bit of the pilot sequences can be multiplied by an N bit
long pseudonoise sequence. The resulting bit sequence may then be used as
the pilot sequence for the pilot subcarrier. The N symbol long pilot
sequence; may be an orthogonal sequence as mentioned above.

[0064]In addition, a PN code can be applied to any of the previously
mentioned schemes that use a distinct pilot subcarrier set for each base
station--for example, schemes 400, 500 and 600 discussed with respect to
FIGS. 4, 5 and 6. In such schemes a unique PN sequence can be generated
and used as the pilot sequence itself for each of the distinct pilot
subcarriers.

[0065]Referring now to FIG. 8, a flow diagram of an illustrative process
800 for transmitting information between an intended source and a
receiver to minimize co-channel interference from at least one
interfering source is shown. Process 800 begins at step 810. At step 810,
pilot subcarriers and data subcarriers are broadcast from the intended
source and interfering sources. The subcarriers may be broadcast in the
form of radio signal 270 (FIG. 2). The sources may be substantially
similar to base station transmitter 200 (FIG. 2). The frequency reuse of
the data subcarriers and the pilot subcarriers may differ according to
any particular design, such as the designs discussed in schemes 400, 500,
600, and 700 with respect to FIGS. 4, 5, 6, and 7. For example, the
frequency reuse of the data subcarriers may be different than the
frequency use of the pilot subcarriers. More specifically, the frequency
reuse of the pilot subcarriers may be fractional, while the frequency
reuse of the data subcarriers may be one. This transmission scheme
compromises true universal frequency reuse, but allows for the design of
the pilot subcarriers to allow for better estimation of the channel. The
pilot subcarriers may be designed according to any of schemes 400, 500,
600, and 700 with respect to FIGS. 4, 5, 6, and 7. The frequency reuse of
the subcarriers as well as the design of the pilot subcarriers may be
achieved by one or more of encoder 220, interleaver 240, and modulator
260 (FIG. 2).

[0066]After the pilot subcarriers and data subcarriers have been broadcast
in step 810, process 800 moves to step 820. At step 820, a signal is
received at the receiver. The receiver may be substantially similar to
mobile station receiver 300 (FIG. 3) A portion of the signal can
correspond to an intended signal associated with the intended source and
an interfering signal associated with the interfering sources as
described with respect to radio signal 370 (FIG. 3).

[0067]Once the signal has been received at step 820, the portion of the
received signal that corresponds to the intended signal is recovered at
step 830. This recovery may be achieved by decoder 320, de-interleaver
340, and demodulator 360 using one or more of the techniques discussed
with respect to FIG. 3.

[0068]Referring now to FIGS. 9-15, various exemplary implementations of
the present invention are shown.

[0069]Referring now to FIG. 9, the present invention can be implemented in
a hard disk drive (HDD) 900. The present invention may implement either
or both signal processing and/or control circuits, which are generally
identified in FIG. 9 at 902. In some implementations, the signal
processing and/or control circuit 902 and/or other circuits (not shown)
in the HDD 900 may process data, perform coding and/or encryption,
perform calculations, and/or format data that is output to and/or
received from a magnetic storage medium 906.

[0070]The HDD 900 may communicate with a host device (not shown) such as a
computer, mobile computing devices such as personal digital assistants,
cellular phones, media or MP3 players and the like, and/or other devices
via one or more wired or wireless communication links 908. The HDD 900
may be connected to memory 909 such as random access memory (RAM),
nonvolatile memory such as flash memory, read only memory (ROM) and/or
other suitable electronic data storage.

[0071]Referring now to FIG. 10, the present invention can be implemented
in a digital versatile disc (DVD) drive 910. The present invention may
implement either or both signal processing and/or control circuits, which
are generally identified in FIG. 10 at 912, and/or mass data storage 918
of the DVD drive 910. The signal processing and/or control circuit 912
and/or other circuits (not shown) in the DVD drive 910 may process data,
perform coding and/or encryption, perform calculations, and/or format
data that is read from and/or data written to an optical storage medium
916. In some implementations, the signal processing and/or control
circuit 912 and/or other circuits (not shown) in the DVD drive 910 can
also perform other functions such as encoding and/or decoding and/or any
other signal processing functions associated with a DVD drive.

[0072]The DVD drive 910 may communicate with an output device (not shown)
such as a computer, television or other device via one or more wired or
wireless communication links 917. The DVD drive 910 may communicate with
mass data storage 918 that stores data in a nonvolatile manner. The mass
data storage 918 may include a hard disk drive (HDD). The HDD may have
the configuration shown in FIG. 9. The HDD may be a mini HDD that
includes one or more platters having a diameter that is smaller than
approximately 1.8''. The DVD drive 910 may be connected to memory 919
such as RAM, ROM, nonvolatile memory such as flash memory and/or other
suitable electronic data storage.

[0073]Referring now to FIG. 11, the present invention can be implemented
in a cellular phone 950 that may include a cellular antenna 951. The
present invention may implement either or both signal processing and/or
control circuits, which are generally identified in FIG. 11 at 952, a
WLAN network interface 968 and/or mass data storage 964 of the cellular
phone 950. In some implementations, the cellular phone 950 includes a
microphone 956, an audio output 958 such as a speaker and/or audio output
jack, a display 960 and/or an input device 962 such as a keypad, pointing
device, voice actuation and/or other input device. The signal processing
and/or control circuits 952 and/or other circuits (not shown) in the
cellular phone 950 may process data, perform coding, and/or encryption,
perform calculations, format data and/or perform other cellular phone,
functions.

[0074]The cellular phone 950 may communicate with mass data storage 964
that stores data in a nonvolatile manner such as optical and/or magnetic
storage devices for example hard disk drives and/or DVDs. At least one
HDD may have the configuration shown in FIG. 9 and/or at least one DVD
may have the configuration shown in FIG. 10. The HDD may be a mini HDD
that includes one or more platters having a diameter that is smaller than
approximately 1.8''. The cellular phone 950 may be connected to memory
966 such as RAM, ROM, nonvolatile memory such as flash memory and/or
other suitable electronic data storage. The cellular phone 950 also may
support connections with a WLAN via WLAN network interface 968.

[0075]Referring now to FIG. 12, the present invention can be implemented
in a set top box 980. The present invention may implement either or both
signal processing and/or control circuits, which are generally identified
in FIG. 14 at 984, a WLAN network interface 996 and/or mass data storage
990 of the set top box 980. The set top box 980 receives signals from a
source such as a broadband source and outputs standard and/or high
definition audio/video signals suitable for a display 988 such as a
television and/or monitor and/or other video and/or audio output devices.
The signal processing and/or control circuits 984 and/or other circuits
(not shown) of the set top box 980 may process data, perform coding
and/or encryption, perform calculations, format data and/or perform any
other set top box function.

[0076]The set top box 980 may communicate with mass data storage 990 that
stores data in a nonvolatile manner. The mass data storage 990 may
include optical and/or magnetic storage devices for example hard disk
drives and/or DVDs. At least one HDD may have the configuration shown in
FIG. 9 and/or at least one DVD may have the configuration shown in FIG.
10. The HDD may be a mini HDD that includes one or more platters having a
diameter that is smaller than approximately 1.8''. The set top box 980
may be connected to memory 994 such as RAM, ROM, nonvolatile memory such
as flash memory and/or other suitable electronic data storage. The set
top box 980 also may support connections with a WLAN via a WLAN network
interface 996.

[0077]Referring now to FIG. 13, the present invention can be implemented
in a media player 1000. The present invention may implement either or
both signal processing and/or control circuits, which are generally
identified in FIG. 15 at 1004, WLAN network interface 1016 and/or mass
data storage 1010 of the media player 1000. In some implementations, the
media player 1000 includes a display 1007 and/or a user input 1008 such
as a keypad, touchpad and the like. In some implementations, the media
player 1000 may employ a graphical user interface (GUI) that typically
employs menus, drop down menus, icons and/or a point-and-click interface
via the display 1007 and/or user input 1008. The media player 1000
further includes an audio output 1009 such as a speaker and/or audio
output jack. The signal processing and/or control circuits 1004 and/or
other circuits (not shown) of the media player 1000 may process data,
perform coding and/or encryption, perform calculations, format data
and/or perform any other media player function.

[0078]The media player 1000 may communicate with mass data storage 1010
that stores data such as compressed audio and/or video content in a
nonvolatile manner. In some implementations, the compressed audio files
include files that are compliant with MP3 format or other suitable
compressed audio and/or video formats. The mass data storage may include
optical and/or magnetic storage devices for example hard disk drives HDD
and/or DVDs. At least one HDD may have the configuration shown in FIG. 9
and/or at least one DVD may have the configuration shown in FIG. 10. The
HDD may be a mini HDD that includes one or more platters having a
diameter that is smaller than approximately 1.8''. The media player 1000
may be connected to memory 1014 such as RAM, ROM, nonvolatile memory such
as flash memory and/or other suitable electronic data storage. The media
player 1000 also may support connections with a WLAN via WLAN network
interface 1016. Still other implementations in addition to those
described above are contemplated.

[0079]The foregoing describes pilot design for universal frequency reuse
in cellular orthogonal frequency-division multiplexing systems. Those
skilled in the art will appreciate that the invention can be practiced by
other than the described embodiments, which are presented for the purpose
of illustration rather than of limitation.

Patent applications by Hui-Ling Lou, Sunnyvale, CA US

Patent applications in class Including cell planning or layout

Patent applications in all subclasses Including cell planning or layout